Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$231.98	6.639%	$247.3812	$247.38	$247.40	$247.40
Purchase #2	$127.49	9.600%	$139.729	$139.73	$139.75	$139.70
Purchase #3	$87.77	5.558%	$92.6483	$92.65	$92.65	$92.60
Purchase #4	$175.90	4.503%	$183.8208	$183.82	$183.80	$183.80
Purchase #5	$6.97	3.388%	$7.2061	$7.21	$7.20	$7.20
Purchase #6	$130.88	10.370%	$144.4523	$144.45	$144.45	$144.50
Purchase #7	$190.48	3.356%	$196.8725	$196.87	$196.85	$196.90
7 purchase totals =	$951.47		$1,012.1102	$1,012.11	$1,012.10	$1,012.10